Constant velocity joint

ABSTRACT

A constant velocity joint includes an outer part having a connecting portion and an opening portion and a plurality of axial grooves forming outer raceways, and an inner part having a plurality of axial grooves forming inner raceways. Each outer raceway and inner raceway form a raceway pair, a ball being disposed in each raceway pair. Each raceway pair defines a region in axial cross-section with respect to a groove longitudinal axis conceptually divided into four quadrants. The outer raceway is in the first and second quadrants and the inner raceway is in the third and fourth quadrants. With torque transmission in a first direction, the ball has two contact points in the first quadrant and/or two contact points in the third quadrant, and with torque transmission in a second direction, the ball has two contact points in the second quadrant and/or two contact points in the fourth quadrant.

CROSS-REFERENCE

This application claims priority to German patent application no.102021208526.1 filed on Aug. 5, 2021, the entire contents of which arefully incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to mechanical joints, and moreparticularly to constant velocity joints.

Constant velocity joints, also called homokinetic joints, are used inorder to enable a force transmission or torque transmission from a firstshaft to a second shaft. The first shaft and the second shaft may beattached to each other at an angle. Such constant velocity jointstypically include a joint outer part and a joint inner part includingtorque-transmitting balls disposed therebetween. The joint outer parthas outer ball raceways, extending axially in a groove-shaped manner,that interact with inner ball raceways, extending axially in agroove-shaped manner, of the joint inner part, so that the balls areeach guided in a pair of outer and inner ball raceways.

In the known constant velocity joints, seen in axial cross-section withrespect to the longitudinal axis of the grooves, each ball has a singlecontact point with the outer ball raceway and a single contact pointwith the inner ball raceway. Due to these single contact points, thepressure exerted by the ball onto the respective ball raceway is veryhigh, which can lead to high loading on, and therefore possibly earlywear of, each ball raceway.

SUMMARY OF THE INVENTION

It is therefore the object of the present invention to provide aconstant velocity joint that has an improved wear behavior and thus anincreased service life.

A proposed constant velocity joint includes a joint outer part having aconnecting side, an opening side, and a plurality of axially extendinggrooves that form outer ball raceways, and a joint inner part includinga plurality of axially extending grooves that form inner ball raceways.Each individual outer ball raceway and inner ball raceway form a racewaypair, wherein a ball is respectively disposed in each raceway pair.

The balls serve for force and torque transmission between the jointouter part and the joint inner part. In this way, the torque of a shaftthat is connected to the joint outer part can be transmitted to a shaftthat is connected to the joint inner part. Due to the axially extendingball raceways, the two joint parts can additionally be tilted against orwith respect to each other. Such a tilting leads to a movement of theballs in the ball raceways.

As discussed in the Background, with conventional constant velocityjoints, the balls contact each ball raceway at a single contact point,which leads to a high contact pressure on each of the two contactpoints. In comparison thereto, in order to now achieve a betterdistribution of the contact pressure and thus a lower load of the ballraceways, the ball raceways of the present constant velocity joint areconfigured such that two contact points are active for each ball racewayof the joint inner part and/or of the joint outer part. This means that,with the present design, each one of the inner joint part or the outerjoint part has two contact points with each ball. Under such designconditions, four contact points are ideally active, two per each ballraceway. Depending on the bend angle of the constant velocity joint,more contact points can also be active, for example, four per ballraceway.

In each case, a better contact-pressure distribution is achieved, sinceat least two contact points are active for each one of the ballraceways. In order to achieve this contact-pressure distribution, theouter ball raceway and the inner ball raceway of a raceway pair define aregion that, in cross-section with respect to the longitudinal axis ofthe grooves, is conceptually divided into four quadrants, wherein theouter ball raceway is disposed in the first and second quadrants, andthe inner ball raceway is disposed in the third and fourth quadrants.With a torque transmission of the constant velocity joint in a firstdirection, the ball has two contact points in the first quadrant and/ortwo contact points in the third quadrant. With a torque transmission ofthe constant velocity joint in a second direction, the ball has twocontact points in the second quadrant and/or two contact points in thefourth quadrant.

Specifically due to the ideal or preferred four contact points, thecontact between the balls and the joint inner part and/or the jointouter part presumably worsens, for example, due to a higher proportionof sliding. However, this expected worsening is more than compensatedfor by the reduction of the contact pressure, so that a moreadvantageous contact situation is established. The special design of theconstant velocity joint, wherein under the design conditions at leastone of the joint parts (inner or outer) has two contact points with theball, leads to a reduced load and thus to less wear, less surfacedamage, lower maximum contact pressure, longer service life, lowerfriction between ball and joint part, lower weight, and furthermoreoffers the possibility for downsizing or shrinking.

The two contact points per ball raceway can preferably be achieved bythe outer ball raceway having, in the first quadrant, a first and asecond radius of curvature whose center points are offset with respectto each other, and/or having, in the second quadrant, a third and afourth radius of curvature whose center points are offset with respectto each other. The curvature of the ball raceway preferably changes bothin the first quadrant and in the second quadrant. However, it is alsopossible that the curvature changes only in one of the quadrants, andthe curvature experiences no change in the other quadrant. Such a changeof the curvature, due to the two radii of curvature having differentcenter points, causes the ball to contact the ball raceway in thecorresponding quadrant at two contact points. Depending on the directionof the torque transmission, the ball preferably has two contact pointsin the first or in the second quadrant.

In an analogous manner, the inner ball raceway can have, in the thirdquadrant, a first and a second radius of curvature whose center pointsare offset with respect to each other, and/or, in the fourth quadrant, athird and a fourth radius of curvature whose center points are offsetwith respect to each other. It can thus be achieved that the curvatureof the inner ball raceway changes both in the third quadrant and in thefourth quadrant. It is also possible here that the curvature changesonly in one of the quadrants, and the curvature in the other quadrantexperiences no change. This change of the curvature, due to the tworadii of curvature having different center points, causes the ball toalso contact the inner ball raceway in the respective quadrantpreferably at two contact points (depending on the direction of thetorque transmission, in the third or in the fourth quadrant).

According to a further embodiment, the outer and/or the inner ballraceway are configured such that the first and the second radius ofcurvature are configured such that one of the two contact points lies inthe region of the first radius of curvature, and the other of the twocontact points lies in the region of the second radius of curvature.Additionally or alternatively, the third and the fourth radius ofcurvature are configured such that one of the two contact points lies inthe region of the third radius of curvature, and the other of the twocontact points lies in the region of the fourth radius of curvature.

Due to these preferably two radii of curvature per quadrant and theirspecific arrangement, it can be insured that under the design conditionsthe ball has four contact points with the ball raceways. The radii ofcurvature of the ball raceways can be different or identical.

According to a further embodiment, the radii of curvature are identical.This leads to a symmetric separation of the radii of curvature and theircenter points on the four quadrants. Due to this symmetric arrangement,the load is uniformly distributed on the four contact points between theballs and the ball raceways.

According to a further embodiment, the contact points are disposed in arange of ±10°, preferably ±5°, about the transition between the firstand the second radius of curvature and/or about the transition betweenthe third and the fourth radius of curvature. The contact points betweenthe ball and the ball raceways can vary within this region depending onthe use case.

The contact points can be disposed symmetrically about an axis that isdefined between the center point of the ball and the transition betweenthe first and the second radius of curvature, and or about thetransition between the third and the fourth radius of curvature.Alternatively the contact points can also be disposed asymmetricallyabout this axis, for example, +10° and −5° or +5° and −10°.

This applies respectively for the outer and the inner ball raceway,wherein the radii of curvature and angles of the outer ball raceway candiffer or can be identical.

According to a further embodiment, in the first quadrant the outer ballraceway is divided by the first and the second radius of curvature intotwo identical parts, and/or in the second quadrant by the third and thefourth radius of curvature into two identical parts.

In an analogous manner, in the third quadrant the inner ball raceway canbe divided by the first and the second radius of curvature into twoidentical parts, and/or in the fourth quadrant by the third and thefourth radius of curvature into two identical parts.

This uniform separation of the ball raceways also contributes to auniform distribution of the contact points. In this way the contactpressure can be uniformly divided, and the contact stresses, and thusthe wear, the friction, and other surface damage can thereby be reduced.

Alternatively it is also possible that the ball raceways are not dividedinto identical parts by the radii of curvature in the respectivequadrants. Furthermore, the separation from quadrant to quadrant can bedifferent.

Further advantages and advantageous embodiments are specified in thedescription, the drawings, and the claims. Here in particular thecombinations of features specified in the description and in thedrawings are purely exemplary, so that the features can also be presentindividually or combined in other ways.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

In the following the invention is described in more detail using theexemplary embodiments depicted in the drawings. Here the exemplaryembodiments and the combinations shown in the exemplary embodiments arepurely exemplary and are not intended to define the scope of theinvention. This scope is defined solely by the pending claims. In thedrawings:

FIG. 1 shows a sectional view of a constant velocity joint;

FIG. 2 shows a perspective view of the joint inner part of FIG. 1 ;

FIG. 3 shows a sectional view of the constant velocity joint of FIG. 1along the sectional plane Y-Y; and

FIG. 4 shows a sectional view of the constant velocity joint of FIG. 1along the sectional plane Z-Z.

DETAILED DESCRIPTION OF THE INVENTION

In the following, identical or functionally equivalent elements aredesignated by the same reference numbers.

FIG. 1 shows a constant velocity joint 1 including a joint outer part 2and a joint inner part 4. The joint outer part 2 can be connected by aconnecting side or portion 6 to a first shaft (not shown). An openingside or portion 8 of the joint outer part 2 surrounds the joint innerpart 4. The joint inner part 4 can be connected to a second shaft (notshown).

The joint outer part 2 includes a plurality of axially extending grooves9 that each form one of a plurality of outer ball raceways 10, thegrooves 9 preferably being formed in the opening portion 8. The jointinner part 4 also includes a plurality of axially extending grooves 11that each form one of a plurality of inner ball raceways 12. As is shownin FIG. 2 , the joint inner part 4 is preferably formed as a generallystar-shaped ring including the plurality of axially extending grooves11.

In order to make possible a force and torque transmission between thejoint outer part 2 and the joint inner part 4, balls 14 are providedthat can be guided by a cage 16. Each outer ball raceway 10 and aseparate one inner ball raceways 12 form a raceway pair, wherein a ball14 is respectively disposed in each raceway pair.

A torque of the joint outer part 2 is transmitted by the balls 14 to thejoint inner part 4. In this way the torque of a shaft that is connectedto the joint outer part 2 can be transmitted to a shaft that isconnected to the joint inner part 4. Due to the axially extendinggrooves 9, 11 providing the ball raceways 10, 12, the two joint parts 2,4 can additionally be tilted relative to each other. Such a tiltingleads to a movement of the balls 14 in the ball raceways 10, 12.

In conventional constant velocity joints, the balls 14 each contact theball raceways 10, 12 in one contact point on each raceway 10, 12. Incomparison thereto, in order to achieve a better distribution of thecontact pressure and thus lower loading on the ball raceways 10, 12, theball raceways 10, 12 of the present constant velocity joint 1 areconfigured such that with a torque transmission of the constant velocityjoint 1 in a first direction (i.e., a first angular direction), eachball 14 contacts the associated outer ball raceway 10 in two contactpoints P-1, P-2 (see FIG. 3 ), and/or the associated inner ball raceway12 also in two contact points P-5, P-6 (see FIG. 4 ). With a torquetransmission of the constant velocity joint 1 in a second direction(i.e., a second angular direction opposing the first direction), eachball 14 can contact the associated outer ball raceway 10 in two contactpoints P-3, P-4, and/or the associated inner ball raceway 12 also in twocontact points P-7, P-8. Under these design conditions, the ball 14preferably contacts the inner ball raceway 10 and the outer ball raceway12 in four contact points overall, that is, a total of four contactpoints P-1/P-2/P-5/P-6 or P-3/P-4/P-7/P-8. However, depending on thetilting of the joint parts 2, 4, each ball 14 can contact the ballraceways 10, 12 in more or fewer contact points.

The region that is defined by the outer ball raceway 10 and the innerball raceway 12 can be conceptually divided into four quadrants I, II,III, IV (see FIGS. 3 and 4 ). That is, in axial cross-sections withrespect to a longitudinal axis (not indicated) through each groove 9 and11, each outer ball raceway 10 has a first quadrant I and a secondquadrant II and each inner ball raceway 12 has a third quadrant III anda fourth quadrant IV, as discussed in detail below.

In FIGS. 3 and 4 , four contact points “P” are respectively depicted forboth the outer and the inner ball raceway 10, 12. However, depending onthe direction of the torque transmission of the constant velocity joint1, only the contact points P-1, P-2 and P-5, P-6 (first and thirdquadrant I, III), and/or the contact points P-3, P-4, and P-7, P-8(second and fourth quadrant II, IV) are active, since the ball 14 isrespectively pressed from the joint outer part 2 in the one or the otherdirection on the diagonally opposing side of the joint inner part 4.

In order to respectively obtain two contact points P for each ballraceway 10, 12, the ball raceways 10, 12 can have different radii ofcurvature, as is described below.

In the region of the first quadrant I, the outer ball raceway 10 has twodifferent radii of curvature, so that in the region 18 the ball racewayis divided into a region 18 having a first radius of curvature and aregion 20 having a second radius of curvature. In the second quadrantII, the outer ball raceway also has two different radii of curvature sothat in the region of the second quadrant II the outer ball raceway 10is also divided into a region 22 having a third radius of curvature anda region 24 having a fourth radius of curvature.

In a similar manner, the inner ball raceway 12 has different radii ofcurvature, i.e., two different radii of curvature in the region of thethird quadrant III so that the ball raceway 12 is divided into a region26 having a first radius of curvature and a region 28 having a secondradius of curvature. In the fourth quadrant IV, the inner ball raceway12 is divided into a region 30 having a third radius of curvature and aregion 32 having a fourth radius of curvature.

Here the radii of curvature of the outer ball raceway 10 and the innerball raceway 12 are configured such that with a torque transmission in afirst direction the contact points P-1, P-2, and P-5, P-6 are active,and with a torque transmission in the other direction the contact pointsP-3, P-4 and P-7, P-8 are active. In each case, the center points of theradii of curvature of the regions 18, 20 are offset with respect to eachother, the center points of the radii of curvature of the regions 22, 24are offset with respect to each other, the center points of the radii ofcurvature of the regions 26, 28 are offset with respect to each other,and the center points of the radii of curvature of the regions 30, 32are offset with respect to each other.

The radii of curvature can also be identical to one another, and thecenter points of the radii of curvature of the respective adjacentregions in a quadrant I, II, III, IV must only not coincide in order toachieve the specific arrangement of the contact points P-1 to P-8. Inparticular, due to identical radii of curvature a symmetric distributionof the radii of curvature and their center points on the four quadrantsI, II, III, IV can be achieved. Due to this symmetric arrangement, theload is uniformly distributed on the respective four active contactpoints between the ball 14 and the outer and the inner ball raceways 10,12. Alternatively, however, an asymmetric distribution of the radii ofcurvature can be present.

It is also possible that in the outer raceway 10, the center points ofthe radii of curvature of the regions 20, 22 coincide, and the centerpoints of the radii of curvature of the regions 28, 30 of the innerraceway 12 also coincide. In this case the outer ball raceway 10 overallincludes three regions 18 and 20/22 and 24 that have three radii ofcurvature having three center points, and the inner ball raceway 12overall can have three regions 26 and 28/30 and 32 that also have threeradii of curvature having three center points. Here the three radii ofcurvature can respectively be identical, or two radii of curvature canbe identical and one can be different from them, or all three radii ofcurvature can be different from one another.

In particular, the radii of curvature are configured such that thecontact points P-1 and P-2 lie in an angular range α and β,respectively, about the transition between the regions 18 and 20. Theangles α and β can be identical or different and preferably lie in arange of ±10° about the transition between the regions 18 and 20. Thisapplies in the same manner for the contact points P-3 and P-4, which canalso lie in an angular range γ, δ, respectively, about the transitionbetween the regions 22 and 24. Here the angles γ, δ can also beidentical to each other or different, and preferably lie in a range of±10°.

This also applies for the inner ball raceway 12, wherein the radii ofcurvature can be configured such that the contact points P-5 and P-6 liein an angular range α and β about the transition between the regions 26and 28. The angles α and β can be identical or different, and preferablylie in a range of ±10° about the transition between the regions 18 and20. This applies in the same manner for the contact points P-7 and P-8,which can also lie in an angular range γ, δ about the transition betweenthe regions 30 and 32. Here the angles γ, δ can also be identical toeach other or different, and preferably lie in a range of ±10°.

Due to the above-described special design of the ball raceways 10, 12,it can be achieved that the ball 14 always has two contact points, P-1and P-2 or P-3 and P-4, with the outer ball raceway 10, and/or twocontact points, P-5 and P-6 or P-7 and P-8, with the inner ball raceway12. In this way the pressure that is exerted by the ball 14 on the ballraceways 10, 12 can be better distributed on the ball raceways 10, 12.This reduces the pressure on the ball raceways 10, 12 and thus leads tolower wear and a lengthened service life of the constant velocity joint1.

Due to the constant velocity joint 1 described herein, an improved andreduced wear behavior and thus an increased service life of the constantvelocity joint 1 can thus be achieved.

Representative, non-limiting examples of the present invention weredescribed above in detail with reference to the attached drawings. Thisdetailed description is merely intended to teach a person of skill inthe art further details for practicing preferred aspects of the presentteachings and is not intended to limit the scope of the invention.

Moreover, combinations of features and steps disclosed in the abovedetailed description may not be necessary to practice the invention inthe broadest sense, and are instead taught merely to particularlydescribe representative examples of the invention. Furthermore, variousfeatures of the above-described representative examples, as well as thevarious independent and dependent claims below, may be combined in waysthat are not specifically and explicitly enumerated in order to provideadditional useful embodiments of the present teachings.

All features disclosed in the description and/or the claims are intendedto be disclosed separately and independently from each other for thepurpose of original written disclosure, as well as for the purpose ofrestricting the claimed subject matter, independent of the compositionsof the features in the embodiments and/or the claims. In addition, allvalue ranges or indications of groups of entities are intended todisclose every possible intermediate value or intermediate entity forthe purpose of original written disclosure, as well as for the purposeof restricting the claimed subject matter. The invention is notrestricted to the above-described embodiments, and may be varied withinthe scope of the following claims.

REFERENCE NUMBER LIST

-   1 Constant velocity joint-   2 Joint outer part-   4 Joint inner part-   6 Connecting side-   8 Opening side-   9 Groove-   10 Outer ball raceway-   11 Groove-   12 Inner ball raceway-   14 Ball-   16 Cage-   18 Region having first radius of curvature-   20 Region having second radius of curvature-   22 Region having third radius of curvature-   24 Region having fourth radius of curvature-   26 Region having first radius of curvature-   28 Region having second radius of curvature-   30 Region having third radius of curvature-   32 Region having fourth radius of curvature-   P Contact points-   I, II, III, IV Quadrants-   α,β, γ, δ Angles

We claim:
 1. A constant velocity joint comprising: a joint outer parthaving a connecting portion and an opening portion, the opening portionhaving a plurality of axially extending grooves, each groove providingan outer ball raceway; a joint inner part having a plurality of axiallyextending grooves, each groove of the joint inner part providing aninner ball raceway, each one of the outer ball raceways and a separateone of the inner ball raceways forming one of a plurality of racewaypairs; and a plurality of balls, each ball being disposed within aseparate one of the plurality of raceway pairs; wherein the outer ballraceway and the inner ball raceway of each raceway pair define a regionthat, in a cross-section with respect to a longitudinal axis of eachgroove, is conceptually divided into four quadrants; wherein the outerball raceway is disposed in a first quadrant and a second quadrant andthe inner ball raceway is disposed in a third quadrant and a fourthquadrant; wherein with a torque transmission of the constant velocityjoint in a first direction, each ball has two contact points in thefirst quadrant and/or two contact points in the third quadrant; and/orwherein with a torque transmission of the constant velocity joint in asecond direction, each ball has two contact points in the secondquadrant and/or two contact points in the fourth quadrant.
 2. Theconstant velocity joint according to claim 1, wherein at least one of:the outer ball raceway has a first radius of curvature and a secondradius of curvature in the first quadrant, each one of the first radiusof curvature and the second radius of curvature having a separate centerpoint, the center point of the first radius and the center point of thesecond radius being offset with respect to each other; and the outerball raceway has a third radius of curvature and a fourth radius ofcurvature in the second quadrant, each one of the third radius ofcurvature and the fourth radius of curvature having a separate centerpoint, the center point of the third radius and the center point of thefourth radius being offset with respect to each other.
 3. The constantvelocity joint according to claim 2, wherein: the first radius ofcurvature and the second radius of curvature are each configured suchthat one of the two contact points in the first quadrant lies in aregion of the first radius of curvature and the other of the two contactpoints in the first quadrant lies in a region of the second radius ofcurvature; and/or the third radius of curvature and the fourth radius ofcurvature are each configured such that one of the two contact points inthe second quadrant lies in the region of the third radius of curvatureand the other of the two contact points in the second quadrant lies inthe region of the fourth radius of curvature.
 4. The constant velocityjoint according to claim 2, wherein: the two contact points in the firstquadrant of the outer ball raceway are disposed in a range of ±10° abouta transition between the first radius of curvature and the second radiusof curvature; and/or the two contact points in the second quadrant ofthe outer ball raceway are disposed in a range of ±10° about atransition between the third radius of curvature and the fourth radiusof curvature.
 5. The constant velocity joint according to claim 2,wherein: the first quadrant of the outer ball raceway is divided by thefirst radius of curvature and the second radius of curvature into twoidentical parts; and/or the second quadrant of the outer ball raceway isdivided by the third radius of curvature and the fourth radius ofcurvature into two identical parts.
 6. The constant velocity jointaccording to claim 1, wherein at least one of: the inner ball racewayhas a first radius of curvature and a second radius of curvature in thethird quadrant, each one of the first radius of curvature and the secondradius of curvature having a separate center point, the center point ofthe first radius and the center point of the second radius being offsetwith respect to each other; and the inner ball raceway has a thirdradius of curvature and a fourth radius of curvature in the fourthquadrant, each one of the third radius of curvature and the fourthradius of curvature having a separate center point, the center point ofthe third radius and the center point of the fourth radius being offsetwith respect to each other.
 7. The constant velocity joint according toclaim 6, wherein: the first radius of curvature and the second radius ofcurvature are each configured such that one of the two contact points inthe third quadrant lies in a region of the first radius of curvature andthe other of the two contact points in the third quadrant lies in aregion of the second radius of curvature; and/or the third radius ofcurvature and the fourth radius of curvature are each configured suchthat one of the two contact points in the fourth quadrant lies in theregion of the third radius of curvature and the other of the two contactpoints in the fourth quadrant lies in the region of the fourth radius ofcurvature.
 8. The constant velocity joint according to claim 6, wherein:the two contact points in the third quadrant of the inner ball racewayare disposed in a range of ±10° about a transition between the firstradius of curvature and the second radius of curvature; and/or the twocontact points in the fourth quadrant of the inner ball raceway aredisposed in a range of ±10° about a transition between the third radiusof curvature and the fourth radius of curvature.
 9. The constantvelocity joint according to claim 6, wherein: the third quadrant of theinner ball raceway is divided by the first radius of curvature and thesecond radius of curvature into two identical parts; and/or the fourthquadrant of the inner ball raceway is divided by the third radius ofcurvature and the fourth radius of curvature into two identical parts.